1. Technical Field
This disclosure relates generally to an aircraft propulsion system and, more particularly, to a nacelle for an aircraft propulsion system and promoting laminar flow next to the nacelle.
2. Background Information
Achieving laminar flow over an aircraft aerodynamic surface, such as an outer surface of a nacelle, has been a goal for many decades because, in general, laminar flow over an aerodynamic surface results in reduced drag compared to turbulent flow over the same surface. Two strategies include natural laminar flow and active laminar flow control.
Natural laminar flow (NLF) may be provided by shaping the aerodynamic surface in a manner such that laminar flow naturally occurs and is maintained along at least a portion of the aerodynamic surface during all or during targeted flight conditions. Natural laminar flow is advantageous because it does not require any additional hardware or controls. However, there are practical limits to how much laminar flow area can be achieved around the exterior of a propulsion system nacelle.
Active laminar flow control (ALFC) involves modifying airflow over an aerodynamic surface so that laminar flow, which occurs over the leading edge, is maintained over at least a portion of the surface by preventing a trip to turbulent flow. The modification to the air flow for active laminar flow control can take different forms, one of which involves continuously removing low energy air from a boundary layer along the extent of the flow surface to prevent the boundary layer from thickening and eventually tripping to turbulent flow. This has been proposed by using many small holes closely spaced and generally evenly distributed along and across the flow surface with suction to pull air from the boundary layer into the holes in a generally continuous fashion.
While active laminar flow control through removal of the boundary layer air is generally known in the art, it has not been commercially implemented due to several problems.
There is a need in the art therefore for an active laminar flow control system which may be commercially implemented with a nacelle of an aircraft propulsion system.